Rotary index table assemblies for processing workpieces such as disclosed by U.S. Pat. No. 3,718,055 Maier have previously included three annular crown gears, with one annular crown gear mounted on a base of the assembly, with a second annular crown gear mounted on a rotary table of the assembly, and with the third annular crown gear movable into and out of engagement with the base and table mounted crown gears so as to selectively position the rotary table both circumferentially and radially with respect to the rotational axis. This circumferential and radial positioning about the rotational axis results from the fact that the teeth of the crown gears extend radially from the rotational axis and taper inwardly to thereby provide both modes of the positioning. Other rotary index table assemblies which utilize crown gears for positioning are disclosed by U.S. Pat. Nos. 3,889,555 Frank et al. and 4,353,271 Pieczulewski.
Driving rotation of rotary index tables has previously been accomplished by the use of worm gear sets. For example, U.S. Pat. Nos. 3,941,014 Benjamin et al and 4,159,658 Parkinson disclose straight worm gear sets that rotatively drive associated rotary tables during index in association with crown gears that provide positioning after the rotation. Furthermore, machine table movement has previously been provided by double enveloping worm gear sets such as disclosed by U.S. Pat. No. 3,824,892 Bondie et al and, as disclosed by U.S. Pat. No. 4,653,739, has been utilized to provide rotary positioning of a workpiece table. Such double enveloping worm gear sets have surface-to-surface contact as opposed to line contact provided by straight worm gear sets and thus have greater capacity to provide rotational driving of greater loads for the same size unit. Rotational positioning for indexing has also been previously provided by polygonal type drive couplings such as disclosed by U.S. Pat. No. 3,507,169 Signer wherein a rotary drive member having polygon surfaces distributes the driving force.
U.S. Pat. No. 4,380,939 discloses a rotary indexing table which includes wedging rings for providing clamping to prevent table rotation and which is unclamped to allow the indexing rotation. During the rotation, pressurized air is supplied to an annular chamber to lift the table for easier rotation.